The present invention relates to a cylinder liner, and more particularly to a cylinder liner having a dual-phase graphite morphology of nodular (ductile) and vermicular iron comprising the outer diameter of the liner, and a gray and vermicular iron comprising the inner diameter of the liner, and a method of making the same.
Cylinder liners are known in the art and are used in various internal combustion engines such as diesel engines. Generally, cylinder liners are inserted or cast into a bore of a cylinder block of an engine. Cylinder liners are typically adapted for receiving a piston with associated piston rings that move reciprocatingly within the cylinder liner. Accordingly, cylinder liners are subjected to great stresses such as heat and friction that may cause them to wear, crack and break.
However, it is important that cylinder liners provide high strength, high rigidity and high dimensional stability while also exhibiting desirable sliding characteristics with respect to any opponent sliding members such as piston rings. Known cylinder liners have been comprised of various materials such as cast iron and reinforced light metals. To reduce wearing, cracking and breakage, some liners have been coated with heat and wear resistant materials. Other liners have been heat treated by electrical induction devices, which surface hardens the portion of the liner that experiences piston wear or through hardened to provide strength and wear resistance. Yet other liners have been roll burnished, reinforced with various materials such as a ceramic matrix, or alloyed to produce a structure such as bainite or steadite to improve wear resistance.
However, the problems of wearing, cracking, and breaking of cylinder liners remain. Particularly, wherever there is a sharp comer transition from one surface of the liner to another, such as at the liner""s flange to wall transition (e.g. a notch), breaking and cracking are common. Further, the materials and methods used to reduce wearing, cracking and breaking of cylinder liners are quite expensive.
Therefore, there is a need for a cylinder liner with improved wear, crack, and breakage resistance, and that can be manufactured cost-efficiently.
The present invention is directed to an iron cylinder liner whereby the cylinder liner has a dual phase graphite morphology. The outer diameter of the cylinder liner is comprised of nodular/ductile iron and vermicular iron. The ductile iron is quite strong and resistant to fatigue, cracking and breaking. The inner diameter of the cylinder liner, which is the wearing surface of the liner, is comprised of a flake or gray iron and vermicular iron. The gray iron exhibits good wear and scuff-resistant qualities, which are necessary qualities particularly for the inner diameter of the cylinder liner.
In a preferred embodiment, the cylinder liner has a gradual transition from ductile and vermicular iron on the outer diameter for improved strength and fatigue resistance, to gray and vermicular iron on the inner diameter for improved wear resistance. The transition region between the outer diameter and inner diameter is comprised of vermicular iron. The amount of ductile iron used in the liner as compared to the amount of gray iron used may vary depending on the specific application and need. For example, as strength requirements increase, the amount of ductile iron that is used will be increased as well.
The present invention is also directed to a method of making a cylinder liner for use in an internal combustion engine. In a first embodiment, a predetermined amount of a magnesium bearing material is placed into a centrifugal die. A gray base iron is then added to the centrifugal die. The magnesium iron gray bearing material is then spun until solidification is complete, forming the cylinder liner defined above.
In a second embodiment, a predetermined amount of a magnesium alloy such as MgFeSi or NiMg bearing material is placed into a spinner ladle. The magnesium bearing material reacts with the base gray iron poured into the spinner ladle. As a result of the reaction, at least a portion of the gray iron is converted to a composition of nodular iron and vermicular iron. The iron compound is then spun to form the cylinder liner defined above.
The magnesium bearing material is preferably a magnesium bearing alloy. Either method can include the additional step of induction hardening the inner diameter. The inner diameter is preferably induction hardened to a Rockwell xe2x80x9cCxe2x80x9d (Rc) hardness of between about 40 and about 50.
The cylinder liner, as defined above and as produced according to the methods described above, includes vermicular iron at a transition region positioned between the outer diameter and the inner diameter, at a greater concentration than at any region approaching either the inner diameter or the outer diameter.
The invention provides a number of advantages. In particular, tensile strength of the dual phase cylinder liner is significantly greater than the tensile strength of known cylinder liners. Cracking and breaking at the liner transition points are reduced. Moreover, the cylinder liner is produced more cost-effectively than known liners such as coated, reinforced, heat-treated, and roll-burnished liners.